Scientists confirm 1908 Tunguska explosion was caused by a comet

Published: Thursday, June 25, 2009, 10:53 [IST]

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Washington, June 25 (ANI): A new research has confirmed that the mysterious 1908 Tunguska explosion that leveled 830 square miles of Siberian forest was almost certainly caused by a comet entering the Earth's atmosphere.

The research connects the two events by what followed each about a day later: brilliant, night-visible clouds, or noctilucent clouds, that are made up of ice particles and only form at very high altitudes and in extremely cold temperatures.

"It's almost like putting together a 100-year-old murder mystery," said Michael Kelley, the James A. Friend Family Distinguished Professor of Engineering at Cornell, who led the research team.

"The evidence is pretty strong that the Earth was hit by a comet in 1908," he added.

Previous speculation had ranged from comets to meteors.

The researchers contend that the massive amount of water vapor spewed into the atmosphere by the comet's icy nucleus was caught up in swirling eddies with tremendous energy by a process called two-dimensional turbulence, which explains why the noctilucent clouds formed a day later many thousands of miles away.

Noctilucent clouds are the Earth's highest clouds, forming naturally in the mesosphere at about 55 miles over the polar regions during the summer months when the mesosphere is around minus 117 degrees Celsius.

The conclusion that a comet was behind the Tunguska Explosion was supported by an unlikely source: the exhaust plume from the NASA space shuttle launched a century later.

According to the researchers, the space shuttle exhaust plume resembled the comet's action.

A single space shuttle flight injects 300 metric tons of water vapor into the Earth's thermosphere, and the water particles have been found to travel to the Arctic and Antarctic regions, where they form the clouds after settling into the mesosphere.

Kelley and collaborators saw the noctilucent cloud phenomenon days after the space shuttle Endeavour (STS-118) launched on August 8, 2007.

Following the 1908 explosion, known as the Tunguska Event, the night skies shone brightly for several days across Europe, particularly Great Britain - more than 3,000 miles away.

Kelley said he became intrigued by the historical eyewitness accounts of the aftermath, and concluded that the bright skies must have been the result of noctilucent clouds.

The comet would have started to break up at about the same altitude as the release of the exhaust plume from the space shuttle following launch.

In both cases, water vapor was injected into the atmosphere.

According to scientists, the water vapor traveled so far without scattering and diffusing because it got caught in counter-rotating eddies with extreme energy, which made it travel close to 300 feet per second. (ANI)